Lapping machine



Dec. 8, 1964 N. A. RANDALL 3,160,870

LAPPING MACHINE Filed Oct. 23, 1961 United States Patent O 3,16t},87 LAPPENG MACHENE Nathan A. Randail, West Aliis, Wis., assig'nor to Alis- Chalmers Manufacturing Company, Miiwauitee, Wis. Filed Get. 23, 1961, Sei'. No. 146,714 3 Claims. (Cl. 340-265) This invention pertains to a machine for lapping the bearing surfaces of mating elements. The invention is more particularly concerned with such a machine wherein a warning device is provided which indicates when the surfaces being lapped are likely to seize.

Although it is not intended to limit the invention to a machine for lapping the blade roots of a steam turbine, the invention will be described in relation to the lapping of turbine blades since this is one particular area where the machine has solved a long existing problem.

In impulse steam turbines the blade roots are quite frequently formed in the shape of a fir tree having a number of radially spaced tangs simulating the branches of the tree. These tangs fit into radially spaced grooves provided in the turbine spindle. The tangs and grooves present axially extending complementary bearing surfaces. In this manner, a very solid connection is provided between the turbine blades and the turbine spindle. As the spindle rotates, the blades have a tendency, due to centrifugal force, to be flung radially outward from the spindle. This causes the radially `outer surfaces of the blade tangs to bear on the radially inner surfaces of the spindle grooves. If the mating surfaces of these grooves and tangs are not accurately finished, the large centrifugal force will not be equally distributed between all of the grooves and tangs. If there should be a concentration of this centrifugal force on one or two blade tangs, it is quite possible that the blade or groove will crack resulting in a failure of the turbine blade whereby it may be severed from the turbine spindle and be flung outward doing considerable damage to Ithe turbine and surrounding area. Such a failure is not only costly but is extremely dangerous due to the high rotational speed of the turbine blades and the resultant large centrifugal force involved.

It Would, therefore, be desirable to lap the blade root tangs to the spindle grooves so that the load is equally divided between all of the tangsand grooves. However,

lapping turbine blades has been extremely diflicult prior to V applicantis invention because of the close clearances between the mating surfaces of the blade and spindle required by the lapping process. During the lapping process, if there is actual metal to metal contact between the blade and spindle, the two parts may weld together in local areas due to heat caused by rubbing friction. This may so damage the mating surfaces that the blades in some instances must be scrapped. It is, therefore, desirable to provide a means of determining when metal to metal .contact is about to occur slightly before the contact actually takes place or immediately upon contact so that the lapping process can be stopped before the surfaces are damaged. p

It is, therefore, a general object of the subject invention to provide a lapping machinewith a warning device which indicates when metal to metal contact between the mating surfaces is about to take place.

A further object of the subject inventlonis to provide a lapping machine of the hereinbeforedescribed type wherein an electric circuit is provided in series with the ele'rnents to be lapped which circuit includes an indicating device which indicates When the mating surfaces are about to come into contact with one another.

An'additiona'l object of the subject invention is to provide a lapping machine of the hereinbefore described type wherein the lapping compound acts as a'resistancc in the electrical circuit vthereby increasing and decreasing the 3,160,870 Patentecl Dec. 8, 1964 'ice intensity of the signal as the distance between the mating surfaces is decreased and increased, respectively.

A further object of the subject invention is to provide a lapping machine of the hereinbefore described type Wherein the indicating device is a common light bulb which glows brighter as the mating surfaces approach oneV another and `the amount of lapping compound between these surfaces is decreased.

An additional object of the subject invention is to provide a lapping machine of the hereinbefore described type wherein an additional light bulb is connected in the electrical circuit in a manner toglow brightly at all times in order to provide a comparison with the light bulb connected in series with the mating surfaces of the elements to be lapped. p

These and other objects of the subject invention wfll become more fully apparent as the following description is read in light of the attached drawing wherein:

FIG. l is a side elevation of a machine constructed in accordance with the invention;

FIG. 2 is an end elevation of FIG. l; and

FIG. 3 is an enlarged view of the mating surfaces of a turbine blade and spindle shown for purposes of illustration.

For purposes of illustration, the invention is shown in the drawing in condition for performing a lapping operation on the bearing surfaces of a turbine spindle and turbine blades. Referring to the drawing, a turbine spindle 1 is supported above the machine in any conventional manner such as by supports 2. The turbine spindle is `provided with a series of axially extended grooves 3 in which is received a turbine blade root 4. As herein shown in FIG. 2 for purposes of illustration, the turbine blades 6 are fastened together and form pairs which are lapped at the same time. Each blade root 4 is provided with a series of axial extending tangs 7 grouped so that the blade root resembles a fir tree.

Referring particularly to FIG. 2, the turbine blades 5 are rigidly connected to a table 8. This connection may be provided in any conventional manner and is herein shown for purposes of illustration as including wedges 9 having their lower flat surfaces resting on the top of table 8 and having their upper inclined surfaces tangent to the con-V vex outer surface are of the turbine blades. Clamps 11 fit over an integral blade shroud 12 on the outer end of the turbine blades and are rigidly connected to the top of table 8 by means of bolts 13. In this manner the turbine blades 6 are rigidly connected to the top of table 8.

.The table 8 is provided with a subframe or undercarriage 14 having a longitudinally extending angled groove 16 on the under side thereof. A railmember 17 having a complimentary angled flange 18 fits into the angled groove 16 of the undercarriage of the table 8. In this manner the table and undercarriage may be moved in a longitudinal direction on the flange 13 and maintain a very accurate transverse position relative to the spindle 1.

During the lapping process it is necessary to raise-or lower the blades 6 relative to the turbine spindle and.b

any conventional means may be'provided for this purpose. As herein shown for purposes of illustration, two complimentary angled blocks 19 and 21 are provided for this purpose. These blocks have identically angled mating surfaces to permit raising and lowering of the table 8 without changing the angu-lar' position of thef block.

are providedto hold theA block 19 inits adjusted positior'i.w i l areaerol Any conventional means may be provided to cause the table 8 to oscillate relative to the turbine spindle 1. For purposes of illustration, a conventional two wayV hydraulic cylinder 29 is shown attached to a support 31 by means of a pivot vpin 32. A piston rod 33 connected to the piston of cylinder 29 is pivotally connected to a flange 34 provided on one end of the table I8.

An electrical indicating circuit 36 is connected in series with the turbine spindle 1 and turbine blades 6. Any electrically responsive indicating means such Vas a conventional light bulb 37 may be provided in this circuit. A conventional battery 38 connected'in the indicating circuitV 36 provides the current to light the bulb 37 whenV vided therein. It should be noted that both light bulbs' 37 and 41 are identieal and that both receive current V from the same battery so that both ,will glow at the same intensity when there is metal to metal contact vbetween the spindle 1 and blades 6. V

In order to lap the turbine blade tangs 7 to the spindlev grooves 3, the turbine spindle 1 is first supported lin any conventional manner so that its longitudinal axis is parallel to the bed plate 22. The turbine blades 6 are then slipped into the spindle grooves 3 and a wedge (not shown) is driven between the end of Vthe turbine blade roots and into a groove 46 provided in the bottom of the spindle grooves. In this manner the turbine blades 6 are forced radially outward relative ito'the spindle and the tangs 7 come into contact with the mating or bearing surfaces of the spindle grooves. The table 8 is then raised the operator is aware that there is about to be surface to surface contact between the'surfaces of the blade roots and spindle grooves and, therefore, the lapping process is Vstopped and the blades are 'raised slightly until the light bulb ,37 glows vat an intensity substantially less than the intensity of the light bulb 41.

With this arrangement applicant has provided an inexpensive and simple manner 'of determining when seizing is about to take place between surfaces that are being V lapped. It should be understood that the clearances between surfaces such as that shown forv purposes of illustration herein, are so slight that it is impossible to determine when there is actual contact merely by visual inspection. In the past, the operator would not be able to determine exactly when surface .to surface contact took place and for this reason seizing was a problem. With the present simple and inexpensive arrangement, the operator knows when metal to metal contact is about to take place and the machine can be readjusted to insure that seizing will not result.

' It should also be understood that there are a number of differentindicating'devices which could be used in f place of the light bulbs shown herein. One such device would be an ohmmeter. With an ohmmeter there would be no need for the comparison circuit 39. Through trial and error it'could be determined what reading on the ohmmeter would insure that the mating surfaces were at the ideal spacing for lapping.

' in the art that various embodiments are Suggested and to a position closely adjacent to theV outer ends of the 37 will be glowing at its greatest intensity and will be substantially equal to the intensity of the light bulb 41. The table Sis raised slightly by meansv of the block'lg f and bolt 22 until the light bulb 37 reduces intensityb or ceases to glow. When the light bulb 37 ceases to glow k,

or reduces light intensity, the operator is assured that there is no contact between ,theturbine blades and turbine spindle. The table .8 is then moved by the cylinder 29 so that the blade roots 4 are completely removed from grooves and the lapping process begins. Because of bthe insertion ofthe lapping compound between theV surfaces 37 will glow slightly. However, the lapping` compound is, in (effect, a resistance to the flow of current and, therefore, the light bulb 3'7 will not glow as brightlyy as the lightbulb 41 and the operator will know that there is no directmetal to metal contact between the blade tangs and the spindle grooves. -As the* blade roots are moved back md forth over the surfaces of the spindle grooves, the

it is intended to cover all such embodiments coming within the scope of the appended claims.

Having now particularly described and ascertained the nature of myV said invention and the manner in' which it is to be performed, I declare that what:I claim is:

1. A machine for lapping the mating surfaces of ele- Vments including the use of a lapping compound comprising: a first support for holding one of said elements; a second support for holding the other of said elements, said supportsV being positionable to hold said mating surfaces in spaced apart parallel relation to permit insertion otherb of said elements, said relative movement being in *of the blade roots. and turbine grooves, the light bulb I lapping compound grinds the surfaces to a velvet finish. V

After a predetermined number ofV passes through the grooves, the blade roots 4 -are Vlowered a predeterrnined amount Which is indicated by a dial 47 having a pointer in contact With the top of the surface ofthe bloch` 19.

Vto'the amount of said lapping Vcompound between. said mating surfaces; and a'nonvariable indicating means continuously giving an indication which-is identical to the Vindication given Vby said variable indicating means when said elements Vare in physical contact. V

7 V2.V A inachinefor lappingfthe mating surfaces of elements comprising: a firstl support for holding one of said elements; a second' support for holding theother of said elements, said supports being positionable to hold-said mating surfaces in spaced apart-para'llel relation to permit 7 insertion of lapping compounds-therebetween; first means TheV lapping process again isV repeated in thenew lowefrel-V 'position and the operator-again lnotices theV intensity Vat* which the light bulb '37 glows.V If the bulb 37 glows at 'an' intensity close togthe intensity -Vof the lightl bulblfltl.,

formoving said elements in a manner to-'increase and decrease said /sp'acing-V between saidfrnating surfaces; second meansV for moving one ,of said' elements relative to the other of' said elements`, said relative movement being .resistance of said circuit being proportional to the spacing of said mating surfaces; and second circuit means connected in series with said source and including a second indicating means identical to said first indicating means, said second indicating means giving a continuous indication identical to the indication of said first indicating means when the resistance in said first circuit is at a minimum.

3. A machine for lapping the mating surfaces of elements comprising: a first support for holding one of said elements; a second support for holding the other of said elements, said supports being positionable to hold said mating surfaces in spaced apart parallel relation to permit insertion of lapping compound therebetween; first means for moving said elements in a manner to increase and decrease said spacing between said mating surfaces; second means for moving one of said elements relative to the other of said elements, said relative movement being in a plane parallel to the planes of said mating surfaces; first electric circuit means connected in series with said elements and including a source of electric energy and a first light bulb, the brightness of said first light bulb being proportional to the spacing between said mating surfaces; and second circuit means connected in series With said source and including a second light bulb identical to said first light bulb, said second light bulb growing at an intensity equal' to the intensity of said first light bulb When said mating surfaces are in contact.

References Cited in the file of this patent UNITED STATES PATENTS 1,898,133 Liebe Feb. 21, 1933 1,961,764 Horstkotte June 5, 1934 1,996,063 Corkran Apr. 2, 1935 2,256,120 Lovenston Sept. 16, 1941 2,947,120 Baner et al. Aug. 2, 1960 2,981,929 Rizzo et al. Apr. 25, 1961 2,984,953 Neal May 23, 1961 OTHER REFERENCES Publication: Journal of the Franklin Institute, Hersey (citing McKee), pp. 116-117, July 1935. 

2. A MACHINE FOR LAPPING THE MATING SURFACES OF ELEMENTS COMPRISING: A FIRST SUPPORT FOR HOLDING ONE OF SAID ELEMENTS; A SECOND SUPPORT FOR HOLDING THE OTHER OF SAID ELEMENTS, SAID SUPPORTS BEING POSITIONABLE TO HOLD SAID MATING SURFACES IN SPACED APART PARALLEL RELATION TO PERMIT INSERTION OF LAPPING COMPOUNDS THEREBETWEEN; FIRST MEANS FOR MOVING SAID ELEMENTS IN A MANNER TO INCREASE AND DECREASE SAID SPACING BETWEEN SAID MATING SURFACES; SECOND MEANS FOR MOVING ONE OF SAID ELEMENTS RELATIVE TO THE OTHER OF SAID ELEMENTS, SAID RELATIVE MOVEMENT BEING IN A PLANE PARALLEL TO THE PLANES OF SAID MATING SURFACES; FIRST ELECTRIC CIRCUIT MEANS CONNECTED IN SERIES WITH SAID ELEMENTS AND INCLUDING A SOURCE OF ELECTRIC ENERGY AND A FIRST INDICATING MEANS, SAID INDICATING MEANS BEING RESPONSIVE TO CHANGES IN THE RESISTANCE OF SAID CIRCUIT, AND THE RESISTANCE OF SAID CIRCUIT BEING PROPORTIONAL TO THE SPACING OF SAID MATING SURFACES; AND SECOND CIRCUIT MEANS CONNECTED IN SERIES WITH SAID SOURCE AND INCLUDING A SECOND INDICATING MEANS IDENTICAL TO SAID FIRST INDICATING MEANS, SAID SECOND INDICATING MEANS GIVING A CONTINUOUS INDICATION IDENTICAL TO THE INDICATION OF SAID FIRST INDICATING MEANS WHEN THE RESISTANCE IN SAID FIRST CIRCUIT IS AT A MINIMUM. 